Cooling system using deep seawater

ABSTRACT

An object of the present invention is to provide a cooling system using deep seawater capable of reducing the cost. The cooling system using deep seawater includes an water intake pump  2  for pumping up deep seawater from the sea, a heat exchanger  3  for exchanging heat between a coolant and cold energy of the pumped-up deep seawater, a first deep seawater pipe  10  for supplying the deep seawater to the heat exchanger  3  from the water intake pump  2 , and a second deep seawater pipe  11  which is in communication with the first deep seawater pipe  10  and discharges the deep seawater into the sea, wherein the first deep seawater pipe  10  and the second deep seawater pipe  11  are laid in close proximity by a predetermined distance in the ground.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the foreign priority benefit under Title 35, United States Code, §119 (a)-(d) of Japanese Patent Application No. 2014-203409, filed on Oct. 1, 2014 in the Japan Patent Office, the disclosure of which is herein incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a cooling system using deep seawater.

BACKGROUND ART

Deep seawater intake facilities have been operated at a dozen places in Japan, and have also been operated in the United States, France, South Korea, Taiwan and other countries. Among them, the facilities in Japan are mainly for industry use (fishery, agriculture, food, bottled water and the like) of deep seawater, and the number of examples which actively use cold energy is small. However, outside Japan, mainly in isolated islands in the United States and France, large scale plans of district cooling operations using cold energy of deep seawater have been advanced. In these plans, it is common that cold water cooled by heat exchange between the cold water (fresh water) and intake deep seawater (sea water) is supplied to a customer through water conveyance pipe network.

Patent Document 1 describes an air conditioning system, which can cool a heat-exchanged medium by cold energy of deep seawater and further efficiently produce fresh water from the deep seawater.

PRIOR ART DOCUMENTS Patent Literatures

-   [Patent Document 1] -   Japanese Patent Application Publication No. 2011-242036

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

In a technology described in Patent Document 1, a distance to an air conditioner from an intake port of deep seawater is generally long. More specifically, not only a water intake pipe for pumping up deep seawater, but also a cold water pipe to the customer from a water intake plant with a heat exchanger, to which the pumped-up deep seawater is first supplied, are long. Incidentally, fresh water to which cold energy of deep seawater is supplied in the heat exchanger flows through the cold water pipe.

When circulating the cold water between the customer and the water intake plant, a pipe system is, for example, one way about 2 to 3 km and an amount of retained water is large, and thus a volume required for an expansion tank for absorbing thermal expansion of water due to temperature change exceeds 100 m³ in some cases. The expansion tank is heavy, and it is difficult to secure a realistic installation place while a cost becomes enormous.

Further, although the cold water pipe is filled with fresh water during operation, water filling and drainage operation is required several times for a pipe flushing and the like during test operation. Since fresh water is expensive in island regions, there is a problem that test operation cost is also expensive.

The present invention is an invention to solve the above problems, and an object thereof is to provide a cooling system using deep seawater capable of reducing the cost.

Means to Solve the Problem

In order to achieve the above object, a cooling system using deep seawater of the present invention is a cooling system using deep seawater, including a pump (for example, water intake pump 2) for pumping up deep seawater from the sea, a heat exchanger for exchanging heat between a coolant and cold energy of the pumped-up deep seawater, a first deep seawater pipe for supplying the deep seawater to the heat exchanger from the pump, and a second deep seawater pipe which is in communication with the first deep seawater pipe and discharges the deep seawater into the sea, wherein the first deep seawater pipe and the second deep seawater pipe are laid in close proximity by a predetermined distance in the ground. Other aspects of the present invention will be described in later embodiments.

Advantageous Effects of Invention

According to the present invention, it is possible to reduce cost of a cooling system using deep seawater.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a layout diagram showing a cooling system using deep seawater according to a present embodiment;

FIG. 2 is an explanatory diagram showing the cooling system using deep seawater according to the present embodiment;

FIG. 3 is a system diagram showing the cooling system using deep seawater according to the present embodiment;

FIG. 4 is a cross-sectional view showing a laid state of a first deep seawater pipe and a second deep seawater pipe;

FIG. 5 is a system diagram showing another example of the cooling system using deep seawater according to the present embodiment;

FIG. 6 is a system diagram showing a cooling system using deep seawater in a comparative example.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a layout diagram showing a cooling system using deep seawater according to a present embodiment. FIG. 2 is an explanatory diagram showing the cooling system using deep seawater according to the present embodiment. FIG. 3 is a system diagram showing the cooling system using deep seawater according to the present embodiment.

FIG. 1 is a case where the cooling system using deep seawater is applied to an air conditioning system of an airport building which is a customer's building 30 in an island. In FIG. 1, a water intake plant 20 is located on the west side (left side of the drawing) of the island, and the airport building which is the customer's building 30 is located on the east side (right side of the drawing) of the island. The airport building has a heat exchanger 3 and an air conditioning equipment 8 using a coolant (for example, cold water) cooled by the heat exchanger 3. Further, a cooling system in the customer's building 30 has an expansion tank 9.

In FIGS. 1 to 3, the cooling system using deep seawater includes a water intake pump 2 for pumping up deep seawater from the sea, a heat exchanger 3 for exchanging heat between a coolant and cold energy of the pumped-up deep seawater, a first deep seawater pipe 10 which is a forward path for supplying the deep seawater to the heat exchanger 3 from the water intake pump 2, and a second deep seawater pipe 11 which is a backward path in communication with the first deep seawater pipe 10 and discharging the deep seawater into the sea. The first deep seawater pipe 10 and the second deep seawater pipe 11 are laid in close proximity by a predetermined distance (for example, several km) in the ground. The predetermined distance is determined based on temperature of the deep seawater which is discharged into the sea from the second deep seawater pipe 11.

The deep seawater which is pumped up from a water depth of, for example, 800 m through an water intake pipe 1 by the water intake pump 2 disposed in the water intake plant 20, is supplied to the heat exchanger 3 in the customer's building 30 from the water intake plant 20 through the first deep seawater pipe 10. The deep seawater which has been supplied to the heat exchanger 3 is heat-exchanged with the cold water by the heat exchanger 3, and then the deep seawater is returned through the second deep seawater pipe 11, to be discharged into the sea.

In order to suppress temperature rise of the deep seawater supplied to the customer's building 30, a pipe with heat insulation is used as the first deep seawater pipe 10. A HDPE pipe (high-density polyethylene pipe) which is insulated with heat insulating material is used as the pipe with heat insulation. Specifically, the HDPE pipe and a rigid polyurethane insulating material are integrated with a special adhesive, and are covered with the HDPE on the outside thereof. A HDPE pipe without heat insulating material is used as the second deep seawater pipe 11.

Further, both of the first deep seawater pipe 10 and the second deep seawater pipe 11 are buried in the ground in order to suppress thermal expansion and contraction (dot area in FIG. 2). The details will be described with reference to FIG. 4.

FIG. 4 is a cross-sectional view showing a laid state of a first deep seawater pipe and a second deep seawater pipe according to the present embodiment. FIG. 4 is an AA cross-sectional view in FIG. 2. When a plurality of pipes is buried in the ground, the pipes are generally arranged side by side. In contrast, in the present embodiment, the first deep seawater pipe 10 is disposed on the lower side, and the second deep seawater pipe 11 is disposed on the upper side. In order to suppress bending of a pipe during pipe laying operation, a pipe support base 12 is provided to support the pipe, if necessary.

Effects of burying the pipes as shown in FIG. 4 are as follows.

-   (1) Since the forward and backward paths of the deep seawater are     buried one above the other so that a return pipe (the backward path)     is buried above the other pipe, it is possible to suppress     temperature rise of the deep seawater in the forward path. For     example, even if temperature of the ground surface is higher than     30° C., temperature of the deep seawater in the forward path can be     suppressed to about 10° C., when temperature of the deep seawater in     the backward path is 18° C. -   (2) By burying the HDPE pipe, expansion and contraction due to     thermal expansion can be suppressed by a frictional force with soil.     Since the HDPE pipe has a thermal expansion coefficient larger than     that of steel pipe or other metal pipes, there is a possibility that     a joint portion or the like is damaged by thermal expansion and     contraction due to a temperature difference between during     construction (for example, about 30° C.) and during deep seawater     flowing operation (for example, 8° C.). The thermal expansion and     contraction can be physically suppressed. Therefore, it is     economical, for example, because an expansion joint is not     necessary, or the number of the expansion joints can be reduced.

Returning to FIG. 2, a water intake method by the water intake plant 20 will be described. In the deep seawater intake of the present embodiment, the most economical balance between initial cost of the water intake pipe 1 and running cost of the water intake pump 2 is taken into consideration. The water intake pump 2 is installed in a lower position than MSL (Mean Sea Level), so that water pressure (water head pressure) is always applied to a suction port of the water intake pump 2. When the deep seawater flows through the water intake pipe 1, pressure loss (ΔP) is generated by friction with a pipe inner surface. By determining an inner diameter of the water intake pipe 1 so that the pressure loss ΔP is equal to the above-mentioned water head pressure, it is possible to reduce power of the water intake pump 2, thereby reducing the running cost.

Pressure loss of the water intake pipe 1 is obtained by the following calculation formula (1).

Δh=10.67×C ^(−1.85) ×D ^(−4.87) ×Q ^(1.85) ×L  (1)

Here, Δh is friction head loss (m), C is flow rate coefficient, D is pipe diameter (m), Q is flow rate (m³/s), and L is pipe length (m). When it is assumed that C=150, D=0.8 m, Q=0.4 m³/s, and L=2500 m, pressure loss Δh of the water intake pipe 1 is equal to 1.4 m. By installing the water intake pump 2 in a position of −4.0 m from the MSL in consideration of this value (1.4 m) and pressure loss (for example, assumed to be 2 m) of a water intake port, a strainer and the like, the water pressure (water head pressure) exceeding the pressure loss of the water intake pipe 1, the water intake port, the strainer and the like is always applied to the suction port of the water intake pump 2, and thus it is possible to reduce the power of the water intake pump 2, thereby reducing the running cost. Note that, since the pressure loss Δh is proportional to the pipe length L if an amount of water intake is constant, it is necessary to lower the position of the water intake pump 2 (lower a position of a pump chamber), as the water intake pipe 1 is longer.

On the other hand, a water supply pipe (the first deep seawater pipe 10) for supplying the deep seawater to the customer's building 30 from the water intake pump 2 is desirable to increase flow rate by reducing diameter in consideration of cost and temperature rise during water supply. However, when increasing the flow rate, an abnormal vibration is generated by turbulence in the pipe while the pressure loss is increased, and thus the running cost of the pump is increased.

Therefore, the flow rate of the deep seawater pumped by the water intake pump 2 in the pipe is generally set to about 2 to 2.5 m/s from the viewpoint of not generating abnormal vibration. In the present embodiment, when the flow rate is set to the above value, a diameter of the water supply pipe is 630 mmφ, and can be smaller than a diameter of the water intake pipe 1.

FIG. 6 is a system diagram showing a cooling system using deep seawater in a comparative example. The deep seawater pumped up from water depth of 800 m by the water intake pump 2 through the water intake pipe 1 (for example, pipe length of about 3 km) is heat-exchanged with the cold water by the heat exchanger 3 disposed in the water intake plant 20, and then is discharged into the sea through a water discharge pipe 4. The cold water cooled by the heat exchanger 3 is supplied to the customer's building 30 through a first cold water pipe 5 (for example, pipe length of about 3 km), and is used for cooling by the air conditioning equipment 8 in the customer's building 30. The cold water after being used for cooling by the air conditioning equipment 8 is supplied to the water intake plant 20 through a second cold water pipe 6, and is again supplied to the customer's building 30 through the heat exchanger 3 by a cold water pump 7. Pipes with heat insulation are used for the first cold water pipe 5 and the second cold water pipe 6 in order to prevent loss of heat energy. Since the cold water in the first cold water pipe 5 and in the second cold water pipe 6 is thermally expanded due to temperature change, an expansion tank 9 is provided in order to absorb the thermal expansion. A volume required for the expansion tank 9 is proportional to an amount of water retained in a cold water pipe system.

In contrast to the comparative example in FIG. 6, in the present embodiment shown in FIG. 3, the heat exchanger 3 installed in the water intake plant 20 in FIG. 6 is installed in the customer's building 30 in FIG. 3. Accordingly, the first deep seawater pipe 10 and the second deep seawater pipe 11 are provided in place of the first cold water pipe 5 and the second cold water pipe 6 between the water intake plant 20 and the customer's building 30, so that the deep seawater is supplied to the customer's building 30 from the water intake plant 20. The present embodiment in FIG. 3 has following effects compared to the comparative example in FIG. 6.

(1) Since the second deep seawater pipe 11 is provided in place of the second cold water pipe 6 between the water intake plant 20 and the customer's building 30, an amount of the expensive HDPE pipes with heat insulation is reduced, and construction costs are reduced. Meanwhile, since the temperature of the deep seawater which is discharged into the sea through the second deep seawater pipe 11 is raised by receiving heat from the ground, it is possible to discharge the deep seawater into the shallower sea. This allows a water discharge pipe to be short, and thus an effect of reducing the power of the pump is obtained while the construction costs are reduced.

(2) By burying the second deep seawater pipe 11 over the first deep seawater pipe 10, the second deep seawater pipe 11 receives the heat from the ground while the first deep seawater pipe 10 is prevented from being heated by the heat from the ground.

(3) Although the deep seawater filled in the first deep seawater pipe 10 and in the second deep seawater pipe 11 is thermally expanded due to temperature change, an expansion tank is not required because an end of the second deep seawater pipe 11 is open to the sea. A volume required for the expansion tank of the cold water pipe system in the customer's building 30 becomes small. Further, since the deep seawater for filling the pipes is obtained from the sea, fresh water for filling or flushing is not required. As a result, in island regions where fresh water is precious, impact on water resources is also reduced.

FIG. 5 is a system diagram showing another example of the cooling system using deep seawater according to the present embodiment. A difference between FIG. 5 and FIG. 3 is that the second deep seawater pipe 11 is not extended to the water intake plant 20, but the deep seawater is discharged into the sea in the vicinity of the customer's building 30. When discharging the deep seawater into the sea, in consideration of influence on ecosystem in discharge area, it is common that the deep seawater is discharged in a water depth of close temperature as well as in the vicinity of water intake area in order to avoid mixture of different quality seawater. However, when it is determined that the customer's building 30 is close to the sea and there is no problem to discharge the deep seawater into the sea area, the deep seawater is discharged into the sea in the vicinity of the customer's building 30. In this case, since the second deep seawater pipe 11 is significantly shortened, the construction costs are reduced while the power of the water intake pump 2 is reduced, so that energy saving effect can be obtained.

Although the air conditioning equipment 8 using the cold water is shown as an example for the customer's building 30 in the present embodiment, the deep seawater can be applied to multistage use. For example, the cold energy of the deep seawater is used for air conditioning, and the deep seawater after using the cold energy may be further used in a seawater desalination device.

DESCRIPTION OF NUMERALS

-   1: water intake pipe -   2: water intake pump (pump) -   3: heat exchanger -   4: water discharge pipe -   5: first cold water pipe -   6: second cold water pipe -   7: cold water pump -   8: air conditioning equipment -   9: expansion tank -   10: first deep seawater pipe -   11: second deep seawater pipe -   12: pipe support base -   20: water intake plant -   30: customer's building 

1. A cooling system using deep seawater, comprising: a pump for pumping up deep seawater from the sea; a heat exchanger for exchanging heat between a coolant and cold energy of the pumped-up deep seawater; a first deep seawater pipe for supplying the deep seawater to the heat exchanger from the pump; and a second deep seawater pipe which is in communication with the first deep seawater pipe and discharges the deep seawater into the sea, wherein the first deep seawater pipe and the second deep seawater pipe are laid in close proximity by a predetermined distance in the ground.
 2. The cooling system using deep seawater according to claim 1, wherein the first deep seawater pipe and the second deep seawater pipe are laid one above the other in the ground, while the second deep seawater pipe is laid on the ground surface side, and the first deep seawater pipe is laid on the lower side of the second deep seawater pipe.
 3. The cooling system using deep seawater according to claim 1, wherein the first deep seawater pipe is insulated with heat-insulating material.
 4. The cooling system using deep seawater according to claim 1, wherein the predetermined distance is determined based on temperature of the deep seawater which is discharged into the sea from the second deep seawater pipe.
 5. The cooling system using deep seawater according to claim 1, wherein the pump is installed in a position lower than sea level. 